Try this script:

  #!/bin/sh

  IFS='\
  '
  for i in `ls -dLtr \`lsof -c plugin-containe -a -u $USER -X +L1 | awk -F ' +' '/\/tmp\/Flash/{ print "/proc/" $2 "/fd/" gensub("[^0-9]", "", "g", $4); }'\``; do
    PLAY="$PLAY $i"
  done
  IFS=' '
  mplayer -osdlevel 3 -fs $PLAY

I have it bound to a shortcut key in my window manager and I installed http://userscripts.org/scripts/show/13333 to automatically pick 720p videos, and pause them.

So I go to youtube in a tab, let it buffer for a bit, hit the shortcut key and enjoy.

Note that it's only semi-recent versions of flash that automatically delete the videos, if not remove the +L1